Campus Constant Flow Primary/Variable Flow Secondary Chilled Water System Problems
- Chillers will only load to 70%.
- Unable to utilize 100% of installed chiller capacity.
- Chilled water distribution temperature not equal to or less than design of 42 Degrees F when secondary chilled water flow exceeds primary chilled water flow
- Chillers are manually added and subtracted
- Over pumping in decoupler piping (Wasted Pump Energy)
Solution To Problem
See ASHRAE Journal October 2104 Article Titled "Simplified Chiller Sequencing."
The article presents an approah that was implemented for a campus chilled water system with four 1200 ton centrifugal chillers and solved the problems indicated for the chilled water system.
The solution required:
- Installation of Four Primary Pumps with Variable Frequency Drives (VFD)
- Installation of Four Temperature Sensors
- Removel of check valve in decoupler piping
Mixed temperature based calculations were developed and used to control primary pump VFD speed and sequencing control for chillers.
Results of implemented solution:
- Chillers could be loaded to 100% if required
- Chillers are added and subtracted automatically
- Secondary distribbution temperature is controlled to less than design
- Decoupler flow minimized
- Primary chilled water flow equals secondary chilled water flow.